LeetCode: 328. Odd Even Linked List

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328. Odd Even Linked List

LeetCode - Odd Even Linked List

使用双指针，将链表拆分成奇偶数两个链表，然后再拼接！确实是个很棒的方法！

Given a singly linked list, group all odd nodes together followed by the even nodes. Please note here we are talking about the node number and not the value in the nodes.

You should try to do it in place. The program should run in O(1) space complexity and O(nodes) time complexity.

Example 1:

Input: 1->2->3->4->5->NULL
Output: 1->3->5->2->4->NULL

Example 2:

Input: 2->1->3->5->6->4->7->NULL
Output: 2->3->6->7->1->5->4->NULL

Note:

The relative order inside both the even and odd groups should remain as it was in the input.
The first node is considered odd, the second node even and so on …

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/**
 * Runtime: 0 ms, faster than 100.00% of Java online submissions for Odd Even Linked List.
 *
 * Memory Usage: 38 MB, less than 12.50% of Java online submissions for Odd Even Linked List.
 *
 * Copy from: https://leetcode.com/problems/odd-even-linked-list/solution/[Odd Even Linked List solution - LeetCode]
 */
public ListNode oddEvenList(ListNode head) {
    if (Objects.isNull(head)) {
        return null;
    }
    ListNode odd = head;
    ListNode even = head.next;
    ListNode evenHead = even;
    while (Objects.nonNull(even) && Objects.nonNull(even.next)) {
        odd.next = even.next;
        odd = odd.next;
        even.next = odd.next;
        even = even.next;
    }
    odd.next = evenHead;
    return head;
}